Sep. 11, 2013

Pets: They’re cute, cuddly, and convivial. But with furry companionship comes cleanup. Dogs poop 10 million tons each year, reports DoodyCalls, a pet waste pickup service. Domestic and feral cats contribute their share, too, producing 1.2 million tons of feces annually, according to a study published in July in the journal Trends in Parasitology. What’s a pet owner to do with all that poo?

Bagging it up and tossing it in the dumpster may seem like an unfavorable option because the waste ends up sitting in a landfill. But it’s probably the best way to kill infectious organisms that might be lurking in the gunk—or at least keep them at bay.

Dog and cat droppings can contain parasites, including zoonotic hookworms and roundworms. The larvae and eggs can persist in the environment, and people can encounter them if they tread in areas christened by infected pooches and purrers.

Zoonotic hookworm larvae typically wend their way into humans by burrowing into skin, causing inflammation known as cutaneous larva migrans. As larvae die, however, the condition resolves, according to Sue Montgomery, an expert in the CDC’s Parasitic Diseases Branch. Zoonotic roundworms, meanwhile, infect humans if the parasites' eggs are ingested (think, kid playing outside in contaminated dirt). Roundworm larvae—which “wander” through various body organs—usually don’t produce any symptoms in their human hosts, but in some cases they can damage tissue, nerves, or the eye in an infection called toxocariasis.

But before freaking out that any misstep into a stinky pile spells worm disease, take note: While it’s unclear how many people in the U.S. are infected by zoonotic hookworms or roundworms, illness stemming from these parasites isn’t a huge problems these days, says William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University. In developing countries, however, stray dogs and cats often have high rates of hookworm infection, which can lead to widespread sand and soil contamination, according to the CDC.

Cats also play honorary host to another parasite, called Toxoplasmosis gondii. Feline feces can contain the parasite’s oocysts, or eggs, which can cause a disease in humans (and other animals) called toxoplasmosis. Most people infected with T. gondii don’t show signs of illness, however. Those who do might develop inflammation in their lymph nodes or mild, flu-like symptoms. The parasite poses the greatest risk to people with compromised immune systems and infants born to women who were infected during or just before pregnancy (T. gondii can cause developmental abnormalities, as well as mental disabilities and other problems that manifest later in life).

Though most people infected with T. gondii are asymptomatic, this doesn’t mean kitty poo is harmless. The parasite is probably more pervasive and potentially more dangerous than we know, according to the researchers of the Trends in Parasitology study. “There is evidence that accumulating T. gondii oocysts in the environment pose a significant public health hazard,” they write.

Oocysts can survive for months in soil and remain infectious. They can also contaminate and persist for years in both fresh and salt water, according to Patricia Conrad, a parasitologist at the University of California Davis’ School of Veterinary Medicine who conducted a study on sea otters infected with toxoplasmosis from runoff contaminated with cat feces.

Aside from direct contact with oocyst-laden cat poop, people can also inhale or ingest oocysts by gardening in contaminated soil, eating unwashed fruit or vegetables, drinking contaminated water, playing in contaminated sandboxes, or petting dogs that rolled in cat feces.

Properly disposing of pet poo can help prevent associated parasites such as T. gondii from spreading. Composting is a no-no—“It gives parasites a superb breeding ground,” says Craig Prior, a veterinarian and board member on the Companion Animal Parasite Council. While flushing the stuff will probably filter out microbes once it hits the wastewater treatment facility, there’s always a chance the system won’t work properly.

Sealing pet poop in a bag that bakes in a landfill is probably the most favorable option in terms of killing fecal parasites, or at least containing them. “The whole bagging-[poop]-up and sending-it-to-the-landfill is not a perfect solution, but that’s the best recommendation that I have,” says Conrad. “It is good in terms of killing oocysts, but in terms of filling up landfills, that's probably the downside.”

So, the next time Fido or Fluffy do their dirty work, bag it up, and dump it in the trash.